With continuous improvement of urban modernization, power cables, as an important equipment in urban power grid, have been developing at a fast speed. Further, urban power cables are commonly arranged to be laid underground. One of the reasons causing cables failures during practical operations may be faults in a grounding system of power cables, which accounted for 21% of cable failures. The sheath of a power cable may, during usage, be susceptible to external forces, chemical corrosions, lightning overvoltage or system overvoltage, resulting in damaged insulation of the sheath and one or more grounding points, thereby undermining the grounding system of high-voltage cable metal sheath. Induced electromotive force of the cable metal sheath may be unbalanced. The metal sheath and the earth may form a large circulation current. Additional line loss may increase and the cable temperature may increase. When such situation occurs for a long time, the main insulation may be jeopardized and the normal lifespan of cable circuit may be shortened, safety operations of transmission lines are thus affected. To overcome the phenomenon described above, ground cable boxes are commonly used for protection. Further, an online ground current monitoring method may be applied to monitor power-cable ground currents online. After developments in recent years, there are mainly two methods for monitoring ground currents of power cables online.
One method includes pre-configuration and active upload. A monitoring device may be preconfigured with a sampling frequency before installation. The monitoring device may collect data periodically according to the stored preconfigured settings and actively upload the data to a backend database of a monitoring server. The other method includes passive upload upon inquiry. A server in the monitoring center may, based on a frequency set by a user, perform data query and data reading actions on a monitoring device, and record the data in a database. The two strategies may have certain application values, but significant deficiencies still exist. In the first method, sampling is at a fixed frequency. Along with adjustments and changes of power line loads, the first method may not meet the requirements of monitoring power cables in a long term. The other strategy includes controlling the monitoring device to collect and upload data through a backend monitoring server. Although the disadvantage of being unable to adjust sampling frequency is overcome, due to the characteristics of the communication model, corresponding heartbeat signals need to be maintained to keep the links stable, which may increase resource consumption of the server and reduce system expansion performance.